<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div {
      /* 我们需要一个200*200的盒子，但是这个盒子有10像素的红色边框 */
      width: 180px;
      height: 180px;
      background-color: green;
      border: 10px solid red;
    }
  </style>
</head>

<body>
  <div></div>
</body>

</html>